Optical catheters are increasingly used for a wide variety of optical diagnostic procedures and interventions. Accessing tissues via blood vessels, or other orifices, as opposed to by open surgery, reduces damage to the body, facilitating recovery. Generally the finer the catheter, the smaller the blood vessel it can enter. The present invention is particularly suited to providing catheters having small diameters and requiring reliable rotation.
A reliable rotary fibre scanner is a critical part of optical coherence tomography (OCT) systems employed for medical imaging and diagnosis, particularly, to intravascular and cardiovascular applications. In particular up to 70% of heart attacks are thought to be caused by vulnerable plaque in arterial walls. OCT systems with rotary fibres may provide a useful tool to image and analyze the plaques.
Most legacy technologies use a rotary motor at a base end of the fibre outside the body, and rotate the whole fibre to perform the circular scan (e.g. U.S. Pat. No. 6,445,939). As the fibre have lengths around 1.5 m, and the fibers are bent and twisted, and subject to different forces in use, the rotation of the base end does not necessarily correspond to equal angular changes at the inserted end of the catheter, and neither stable nor uniform rotary actuation is provided. In application, the rotation at the inserted end of the fibre suffers from non-uniform movements, which directly results in scanning errors during the measurement (non-uniform rotational distortion). Because those errors appear to be random, it is almost impossible to calibrate and compensate them by post-processing. As scanning techniques require higher precision in terms of positioning and momentum of the inserted end, this technique becomes increasingly problematic. Diameters of typically used optical fibre are ˜150 μm, it is very difficult to make a part to rotate the laser beam emitted from optical fibre. Furthermore a coupling component which passes the light from a non-rotating fibre to a rotating fibre at the base end has been known to pose problems with losses. Time-varying fibre birefringence may also be a problem with this type of scanning technique. This is a known problem in the art, and various solutions have been proposed. For example, U.S. Pat. No. 6,891,984 teaches provision of a viscous damping fluid located within the sheath to provide drag.
A second technique involves placing the motor at a distal end of the catheter (e.g. “Micromotor endoscope catheter for in vivo, ultrahigh-resolution optical coherence tomography” Herz et al. Optics Letters v. 29, No. 9, Oct. 1, 2004, “In vivo three-dimensional microelectromechanical endoscope swept source optical coherence tomography” Su et al. Optics Express v. 15, No. 16, 10390, Aug. 6, 2007, and “Endoscopic optical coherence tomography system” Xiadong et al. Proc. of SPIE v. 6357, 63574B, 2006). This has disadvantages that power and control wires occlude the sensor over part of the radial scan of the device.
Concentric drive endoscopes are also known (“A concentric three element radial scanning optical coherence tomography endoscope” Bonnema et al. J. Biophoton., 2, No. 6-7, 353-356, 2009), but a concentric drive brings with it severe constrains on the flexibility of the endoscope, and is not suitable for passage through winding blood vessels.
Finally MEMS devices with limited rotation have been designed that avoid the above problems, and place a motor near the distal output of the beam, but between the beam exit and the base end (e.g. “MEMS based non-rotatory circumferential scanning optical probe for endoscopic optical coherence tomography” Xu et al. Proc. of SPIE-OSA, v. 6627, 662715-1, 2007; “New endoscope sees what lies beneath” MIT Tech, Rev., Dec. 3. 2009). However such devices introduce several other difficulties, including the diameter, the complexity of the device, and increased optical insertion loss from multiple reflections, the complexity and cost of forming the device, etc.
As power supplies and electromagnetic actuation are all highly problematic, there are limited possibilities for actuation of catheters.
Accordingly there is a need for a catheter having a motorized rotational control at the insertion end, for higher control, but avoids the problems of wires crossing the scanning beam, and provides a reliable, relatively low cost fabrication, assembly, and use.